The repositioning and stabilization of the fragments are typically unplanned surgical procedures. If the patient's condition (e.g., the patient's circulation) is stable, the operator will usually treat the fracture without making use of various aids. Generally, depending on the fracture and number of fragments, different osteosynthesis materials and methods are used. Both plates and intramedullary nails are commonly used. So that the intramedullary nail or the plate can be correctly applied, the fragments have to be aligned and/or repositioned with regard to each other. The quality of the alignment may not be changed post-operatively. For correction purposes the typical option is a further medical procedure. As the bone fragments lie inside the soft tissue of the extremities, they can be accurately repositioned with the help of X-ray image intensifiers. An additional difficulty is the fact that the muscles surrounding the bone contract so that the fragments end up in an unnatural alignment.
In order to correctly align the fragments, forces are applied to the fragments from outside. These are kept constant for the duration screwing the plates or inserting the intramedullary nails.
Imprecise alignment of the fragments results in rather large rotative misorientation of the fragments with regard to each other which can no longer be changed postoperatively. Due to the high cost and medical risk of a corrective procedure, rotative misorientations are largely tolerated, resulting in unsuitable treatment of the patient.
An initial possibility for aligning the bone fracture fragments is to give an assistant physician the task of exerting the forces and repositioning the fragments by pulling and aligning the distal end of the extremity. During this, the operator aligns and fastens the osteosynthesis material with the aid of an X-ray image intensifier. In doing so the assistant physician and operator stand very close to a source of X-rays for a longer period and are therefore exposed to increased radiation. Particularly because of constant small movements by the assistant physician, the X-ray image is constantly updated.
The problem with this is that alignment of the bones can take place with a rotative error which is not detected during the operation. A malposition of up to 15° is therefore considered as acceptable. For the patients, this amounts to for example internal/external rotation of the foot of up to 15°, which postoperatively can lead to complications or increased wearing of the joint.
In the case of a fracture of the lower extremities, a patient can also be placed on an extension table and the distraction forces exerted on the patient via this. The advantage of this is that the repositioning of the extremity is considerably more stable.
A drawback is that pre-operative positioning is laborious and partially contra-indicated in the case of patients with multiple traumas. There have also been reports of unsuitable effects to the nervous system and soft tissue lesions in the perineum. A further possibility is the use of a mechanical external fixator. This is a mechanical device with which the fragments are fixed to each other by means of Schanz screws/Kirschner wires via extracorporeal rods. Systems are known in which the rods can be adjusted by spindles.
A further possibility is the use of robotic assistance systems. Here, usually the distal fragment of the fracture fragments is positioned via suitable fastening or gripper systems in relation to the proximal fragment by way of a robotic system. The disadvantage of this is that this is a time-consuming procedure as the robots (as well as an appropriate optical navigation system) are initialized and registered. In most cases, these processes require 3D X-ray images which can only be produced by CT. Such techniques can therefore be used if 3D X-ray images with reference bodies are available, specialists who can proficiently operate the systems are present on site, and the patient's condition is not at risk/is stable.